Leads implanted in the body for electrical cardioversion or pacing of the heart are generally known in the art. In particular, electrically transmissive leads may be implanted in or about the heart to reverse (i.e., defibrillate or cardiovert) certain life threatening arrhythmias or to stimulate contraction (pacing) of the heart. Electrical energy is applied to the heart via one or more electrodes on the leads to return the heart to normal rhythm. Leads have also been used to sense conditions, materials or events (generally referred to as “sense” or “sensing”) in the body, such as in the atrium or ventricle of the heart and to deliver pacing pulses to the atrium or ventricle. Tachy leads generally can at least sense, pace, and deliver defibrillation shocks. Brady leads can at least perform the combination functions of pacing and sensing the heart. One of the available functions of the pacemaker or the automatic implantable cardioverter defibrillator (AICD) is to receive signals from a lead and interpret signals. In response to these signals, the pacemaker can pace or not pace. The AICD can pace or not pace, and shock or not shock.
Some leads include drug eluting structures proximate the electrodes to deliver therapeutic drugs near the electrode/tissue interface. However, current leads utilize either a drug plug or a drug collar to store and control the release of the drugs. However, as leads become smaller, the size of the drug plugs and collars becomes incompatible with the lead size. Moreover, a higher impedance electrode design is desirable, since it increases the battery life of the implantable device.